1. Field of the Invention
The present invention relates to avoiding or eliminating undesirable resonance induced in a mass transit vehicle by operation of a propulsion system of the vehicle.
2. Description of Related Art
Vibration created by the mechanical resonance of a mechanical system vibrating at a natural or resonant frequency is well known. In a mass transit vehicle, such as an electrically propelled steel wheeled rail vehicle or rubber wheeled vehicle, mechanical resonance can result from interaction between the electrical and mechanical systems of the vehicle during operation of the vehicle. Failure to control the resonance created by these systems can result in the transmission of vibration throughout the vehicle resulting in an uncomfortable ride for a passenger and a reduction in the life-span of the vehicle's drive system.
Systems for canceling vibrations created by mechanical resonance at a natural frequency have been proposed in which the vibration is sensed via an appropriate pick-up and a cancellation signal is created which is a 180 degrees out-of-phase with the sensed signal. The cancellation signal is applied to or near the vibration source thereby canceling, or at least greatly attenuating, the vibration source. U.S. patents disclosing such systems are U.S. Pat. Nos. 4,153,815; 4,417,098; 4,489,441; and 4,566,118. Such systems are based on adaptive signal processing techniques which may result in an inherent instability which could amplify rather than attenuate the vibration. Also, such systems require direct measurement of a synchronizing signal which provides them directly with the value of the frequency of the excitation source (vibration). These systems operate on the basis of synthesizing the vibration source signal, synchronizing it with the excitation signal, then delaying such signal to achieve a 180 degree phase difference and applying it to cancel the effect of the excitation source. This results in a high sensitivity and potentially unstable vibration cancellation due to exact phasing needs.
Another system involves sending a natural frequency vibration to a band-pass filter or through software, which then outputs an appropriate signal to mechanical actuators configured to act upon the outside forces causing the vibration thereby reducing the extent of the offending vibration. This system is disclosed in U.S. Pat. No. 6,186,485 to Kawazoe wherein a reference signal indicative of a vibrating condition of a vehicle's body and a residual vibration signal indicative of a residual vibration of the vehicle's mounting body are generated. A low-pass filter then generates a driving signal according to the reference signal and the residual vibration signal. This driving signal is output to an actuator in order to reduce vibration transmitted from the vehicle's vibrating body to the vehicle's mounting body. The drawback to such a system is that it relies on a mechanical apparatus to attenuate the resonance.
The aforementioned systems operate on the principle of providing resonance attenuation external to the control loop of a system. In systems where resonance remains within the control loop, such as a rail vehicle control loop, the mechanical resonance leads to a noticeable vibration resulting in an uncomfortable ride for a passenger and a reduction in the life-span of the vehicle's drive system components. Accordingly, what is needed and has not heretofore been developed is a method and apparatus for damping mechanical and electrical resonance as it occurs within the control loop of the system.